The wheels/speed are department of transportation rules. If you want to legally put the car on the road (thus have access to the road) it needs to meet those specs.
Also, I saw a few "sport trikes" that looked like racing bikes but with two front wheels. Looked pretty cool.

As for solar power: My opinion is, it is great for the individual, but bad for the general public.
What does that mean? Most people who own homes have enough land/roof to produce enough solar power to meet their own needs. Some light manufacturing (warehouses) and schools, perhaps even malls/walmarts could do it as well. But per kilowatt hour it is to expensive for heavy energy usage companies, and for society as a whole. Additionally, in order to make a real dent in energy, we would have to cover a large amount of the county with solar panels, and they would only work during the day.

Essentially, I see a future where solar and wind supplement hydro and nuclear power for commercial energy production. Perhaps someone will figure out something new, or increase efficiencies, but only some areas are perfect for wind and solar. Almost all of the good rivers have been dammed up for hydro, but a nuclear power plant can be build anywhere (within reason) and if carefully monitored does not directly emit anything into the environment. Plus the waste that is produced can be shipped and stored anywhere (maybe inside a mountain in the middle of the nevada desert?).